Intro to geology
Two types of Ion
cation, anion
Change from Brittle to Ductile
causes S-wave velocity to decrease
Changes in the chemical compositon beween layers
create changes in density
4 layers of Earth
crust, mantle, outer core, inner core
Compound
substance formed by the chemical combination of two or more elements in definite proportions
Resistance is tied to
density of the material
Magma doesn't always form when continental plate meets continental, but if minor subduction occurs
magma can form and will be felsic
Lava
magma that has reached the surface- still molten, not yet solidified to rock
Nonmetalic
-
We can reconstruct the rates and history of plate motion based on:
--hot spots --orientation of magnetic minerals
Amphiboles
-2 non perpendicular cleavage planes at 60 and 120 -2 single chaines liked by oxygens= ouble chain
Ring of Fire
-A major belt of volcanoes that rims the Pacific Ocean -Locations of earthquakes and volcanoes tned to coincide with seafloor topopgraphy
Continental Crust
-has high silica -has low density -Oceanic is thicker
Electrons fill up _____ surrounding the nucleus
energy levels
Ionic Bond
with electrons transferred
Locations where sediments are deposited: Shoreline (where land meets water)
• Medium-energy transport • Medium grain sizes deposited
Convergent plate boundaries
• Oceanic-oceanic → mafic • Oceanic-continental → intermediate to felsic • Continental-continental → felsic (if any)Hot spots
Divergent plate boundaries
• Oceanic-oceanic → mafic, ultramafic• Continental-continental→ felsic, then intermediate, then mafic
organic sedimentary rock
• Organic carbon-rich plant remains are buried relatively fastSwamp plants (~45% carbon)turn into Peat (~50% carbon) turn into Lignite (~70% carbon)turn into Coal • Bituminous (~80% carbon) • Anthracite (~98% carbon; actually a metamorphic rock)
Shale, Claystone
• Sedimentary rocks formed from clay • Cannot see particles with naked eye • generally deposited in quiet waters - lakes, lagoons, swamps or deep ocean bottom - If black, less oxygen in water - If red, more oxygen in water Shale breaks along bedding planes, claystone does not
Magnetic Field Reversals
• The variations of fluid movement in the outer core also make it possible for Earth's magnetic field to spontaneously reverse itself • i.e. magnetic N and magnetic S can be flipped Step 1: Normal orientation Prior to Reversal Step 2: Beginning of magnetic Reversal Step 3
Hot spots
• under oceanic crust → mafic • under continental crust → intermediate to felsic
Chemical sedimentary rocks
●Dolostone ●Ironstone (aka iron formation) ●Evaporite
Biological Sedimentary Rocks
●Limestone (calcite-based) ●Chert (silica-based) ●Organic (organic carbon-based) ●Phosphorite (phosphate-based)
Basaltic lava types:
●aa ● pahoehoe ● pillow Lowest silica content, lowest viscosityCommon at hot spots and mid-ocean ridges
The Breakup of Pangea
- Divergence of North America & Africa, formation of the Atlantic Ocean (Late Triassic) - Divergence of Antarctica, India, and Australia from South America and Africa (Jurassic) - Divergence of South America and Europe. Convergence of Europe and Africa. Divergence of Australia and Antarctica (Late Cretaceous)
Igneours Rocks can be indentified by Composition
- Felsic = high silica content (light color) - Mafic = low silica content (dark color)
divergent plate boundary
- Lithospheric plates move apart • form rift zones (continental-continental divergence)- example: East Africa • form oceanic ridges (oceanic-oceanic divergence) - Mid-Atlantic Ridge - Upwelling of asthenosphere at plate boundary injects molten mantle material to the surface, forming new oceanic crust• When new crust forms, it forces plates apart
Cinder Cones
- Minor explosive volcano - Mostly pyroclastic discharges of varying sizes - Pyroclastics build up around the vent creating cones- Example: Paricutin, Mexico; Cerro Negro, Nicaragua
Transformation Boundaries
- Plates "slide" past each other, side by side - Can offset oceanic ridges, breaking ridges up into short segments- separate continental plates • Example: San Andreas Fault, California and Mexico
Compression P Waves
-push-pull motion -travel through both solids and liquids -faster velocity
Identifying Minerals
-Analyze the mineral compositon -Measure crystal structure and symmetry -Observe physical properties
Why is the outer core liquid?
-Chemistry changes from a solid peridotite-based composition in mantle to an Fe and Ni based composition -Temperature is too high for Fe+Ni to be solid
Color
-Color of a mineral as viewed by the naked eye -Addiotnal information ussually needed
4) Volcanic Domes
-Composed of rhyolite, but can cause andesite lavas as well • Too viscous to flow - material oozes out to surface from a tube close to the vent • may explode as nuee ardente: a cloud of gas and ash---------Commonly occur at subduction zones after stratovolcano eruptions, hot spots under continents, and continental rifts--Vary in size
Earth's magnetic field
-protects us from harmful solar radiation -Without convection there is no magnetic field and radiation from sun would strip away the atosphere
Fissures
-Long, nearly vertical cracks where basalt lava emerges at large volumes -Fissures are where new crust is created at divergent plate boundary
seismic tomography
-Mapping S-waves (seismic tomography) indicates variations in temperature within the mantle, which are associated with mantle convection
Olivine
-No Cleavage -No oxygen atomsshared between tetrahedra -Major mantle mineral in peridotite
Element
-Number if protons dictates the chemical element -Elements are building blocks
Continental Drift Hypothesis Objections
-One of the major objections to the continental drift hypothesis was its inability to provide an acceptable mechanism for the movement of continents. -Wegner thought that the tidal influence of the moon could move the continents
P-Waves also have shadow zones
-P-waves refract at the outer core
Geodynamo
-Rapid motion of the liquid outer core stirs up electrical flow in the solid (iron) inner core, causing Earth's magnetic field. -Driven by outer core convection
Atoms
-Smallest Unit of matter an element can dividedwhile still retainging the chemical characteristics of that element -Composed of a nucleus surrounded by electrons
Impact of Earths Magnetic Field
-When magnetic minerals drop below their Curie temperature during solidification, they are aligned in the direction of an applied magnetic field (e.g. the Earth's magnetic field) -When magnetic iron emerges from the mantle at divergetingplates, it aligns with Earth's magnetic field before solidifying into rockAs the plates spread, rocks move away in both directions. A symmetric pattern occurs on both sides of the boundary, showing magnetic orientation through time
Hadeon Eon (4.6-3.8 billion years ago)
-accretion of the Earth from celestial debris -frequent celestial collision events -formation of the moon -water vapor condenses into liquid, forming ancient seas -formation of early atmosphere by de-gassing
Oceanic Crust
-has low silicia -has high density -Oceanic is thinner
Volcano
-location where materials from Earth's interior are extruded tothe surface of the Earth • Pyroclasts• Gases- Water vapor, CO2, SO2, H2S, HF• Sound - 1883 eruption of Krakatoa (Indonesia) heard 3,000 miles away• "loudest sound in history" LithosphereSide ventPipe Central ventLava flowsMagmachamberMagma, which originates in the asthenosphere ...... rises through the lithosphere to forma crustal magma chamber.As pressure builds, lavas and/or pyroclasts erupt through a central vent and side vents, ...... accumulating onthe surface to buildthe volcano.Standard model of a volcano Types of lavas1. Basaltic lavas• Highest temperature (1000−1200ºC)• Lowest viscosity• Form basalt igneous rock (mafic)2. Andesitic lavas• Intermediate viscosity, temperature
clastic sediments
-particles produced on Earth's surface resulting from the breakdown of rocks at the surface. -Sediments can be individual minerals or smaller pieces of rock
Seafloor Spreading
-seperation of liospheric plates at mid ocean ridges -Plates must be destroyed at the edge by subduction at convergent plate boundaries to balance out the creation of new oceanic crust
Shear S waves
-side to side motion -travel only through solids slower velocity
Cleavage
-the tendency of a mineral to break along flat surfaces -Bonding forces between atoms not equal in all directions whic creates planes of weakness along which the mineral tends to break -minerla strongly bonded in all directions such as quartz and garnet have no cleavage -weak bonds= good cleavage
Two main types of Igneous Rocks
1) Plutonic/Intrusive rocks - magma cools within the crust and does not make it to surface; cooling is slow 2) Volcanic/Extrusive rocks - magma reaches the Earth's surface as lava flows or explodes as pyroclastic fragments; cooling is fast
Density is dependent on
1. Chemistry 2. Pressure and temperature
Divergent Valley process
1. Continental Rift Valley 2. Water fills in rift valley and forms narrow seas/lakes 3. Larger seas begin to form and new oceanic crust begins to form 4. what started as continental divergence is now oceanic divergence Ex: Arabian plate and African plate
P waves indicate two types of crust
1. Oceanic crust = low silica (Si) = high density = faster P-waves (~7 km/s) 2. Continental crust = high silica = low density = slower P-waves (~6 km/s)
Most fatalities from volcanic eruptions associated with:
1. Pyroclastic flows = avalanche of ash and volcanic debris2. Indirect effects (mostly famine)3. Tsunamis
Steps for turning clastic sediments into sedimentary rock:
1. Weathering 2. Erosion 3. Deposition / Sedimentation 4. Burial and compactionORCementation 5. Diagenesis / Lithification
Types of volcanoes
1. shield volcanoes 2. stratovolcanoes 3. cinder cones 4. volcanic domes 5. fissures
Pyroxenes
2 perpendicualr cleavage planes at 90 angles 2 oxygen atomes
Earth's center is about _____ deep
6400 km/ 4000 miles
Volcanic Bomb
= large, solidified lava extruded from volcano
Hardness
A measure of how easily a mineral can be scratched High Hardness=less easily scratched -Depends on: -Size -Charge -Packing -Mohs Hardness Scale: higher number can scratch lower
Anion
A negatively charged ion
Cation
A positively charged ion
Ion
An atom or group of atoms that has a positive or negative charge.
Pluton
Any magma that has intruded and solidified into rock at depth
Convergent Plate Boundaries
Areas where plates move toward each other and collide, causing uplift. Three Types: - Lithospheric plates move toward each other • Continental-oceanic - examples: Oregon/Washington; Andes Mountains (west coast South America) • Oceanic-oceanic - examples: Japan; southern coast of Alaska • Continental-continental- example: Himalaya Mountains (between India/China)
Sandstones (in particular) are also classified by mineral composition Four major compositional groups:
Arkose = feldspar-rich Quartz arenite = quartz-rich Lithic = particles of other rocks, rather than minerals Graywacke = a sandstone cemented with clay mineral matrix (kaolinite)
Volcanism and the Atmosphere
Ash and gas entering atmosphere can cause climate changes Short term example:Mt Pinatubo eruption in 1991 Long term example:Siberian traps 251-250 mya
Theory of Plate Tectonics
By the 1960s, the continental drift hypothesis evolved into the theory of Plate Tectonics ➢The crust is broken up into rigid lithospheric plates ➢Plates are moving, not the continents themselves ➢Driven by mantle convection causing seafloor spreading
Main siliciclastic rocks based on texture:
Clay becomes shale or claystone Clay + silt becomes mudstone Silt becomes siltstone Sand becomes sandstone Gravel becomes conglomerate or breccia
Nucleus
Control center of the cell, composed of protons and neutrons
What drives plate tectonics?
Convection in mantle upwells heat and magma from mantle to surface at divergent plate boundaries- New oceanic crust formed as old crust pushed away from spreading centers
Bioturbation Structures/ Trace fossils
Evidence that living organisms were present without any remains of the organism
Mineral Composition: Four total compositional groups, based on chemistry of the source magma (mainly silica content):
Felsic igneous rocks (high silica) Intermediate igneous rocks (medium silica) Mafic igneous rocks (low silica) Ultramafic igneous rocks (very low silica)
Igneous Rocks
Form directly from cooling of magma or lava. Ex: granite (magma) and obsidian (lava)
Chemical sedimentary rocks
Formed by chemical processes NOT involving living things
Clastic sedimentary rocks
Formed from clastic sediments
Gases extruded from volcanoes cause ___________ from where trapped gases have escaped; common in basalt and pumice
Gases extruded from volcanoes cause vesicles (bubble holes) from where trapped gases have escaped; common in basalt and pumice
Graded Bedding
Gradual change of one sediment size into another; coarser/heavier sediments are deposited firstExample from underwater landslides (turbidity currents)
Volcanism and the hydrosphere
Groundwater that comes in contact with magma is heated, forming: fumarole - vents emitting steam geysers - vents emitting hot water
Shield volcanoes
Large, flat, shield-like shape • larger area relative to height - Form basalt lava; thin basalt flows build up over time- Most common at hot spots - Relatively predictable and "quiet" eruptions- Examples: Hawaiian Islands (Kilauea; Mauna Loa)
At intraplate hot spots, mantle material directly affects interior of the plate
Mafic igneous rocks form when hot spot is under oceanic crust
Cross-bedding
bedding on an angle to the main bedding plane
Example of Ionic Bond
Na+ and Cl- = NaCl
Benefits of volcanoes
Natural resources for humans • Main sources of metal and sulfur ores • Geothermal energy Provide nutrients to ecosystems living around volcano
Electrons
Negatively charged particles that orbit the nucleus
Earth's Magnetic Field
Orientation of magnetic "compass needle" will vary depending on latitude
Feldspars
Orthoclase feldspar AKA potassium felspar AKA microcline • KAlSi3O8 • Pink-ish/orange-ish • Plagioclase feldspar• (Ca,Na)AlSi3O8 • white • All 4 oxygens shared• 2 cleavage planes at 90°
Three types of Seismic Waves
P waves, S waves, surface waves
Inner Core
P-waves abruptly increase in velocity at around 5150 km depth where core becomes solid Solid because pressures are soimmense that Fe and Ni composition solidifies, and density increases
Two things can happen when waves encounter a change of density :
Reflection = wave will "bounce" off the boundary Refraction = wave will continue through the boundary, but at a different velocity
As pressure increases with depth, less and less peridotite can be melted, so
S-wave velocity increases again
Quartz
Sio2 -All 4 oxygens shared -No Cleavage -Color varies
Igneous Rocks can be identified by texture
Texture = size of mineral crystals - Phaneritic = coarse/large (slow cooling) - Aphanitic = fine/small (fast cooling) - Porphyritic = mix of large and small (fast for some minerals, slow for others) - Glassy = no crystals (super fast cooling)» 2 types: "Frothy" and "Compact"
Example of Magnmatic Intrusion
The Palisades Intrusion
continental drift
The hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations 1. "Jigsaw-puzzle" fit-shapes of continent appear to fit together 2. Rock sequences-similarity of rock assemblages and ages across oceans 3. Fossil assemblages 4. Glacial evidence
Subduction
The process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary.
Country Rock
The rock into which the magma has intruded is
Luster
The way a mineral reflects light Two major categories: Metallic and Non Metallic
Planetary Differentiation
This is a process in which more dense materials of a planet sink to the center, while less dense materials stay on the surface.
San Andreas Fault
Transform boundary between Pacific Plate and North American Plate (California, Mexico); continental-continental
The outer core must be liquid
True
A P-wave that crosses the Moho will be recorded on a seismograph before a P-wave that remains in the crust
True!-P-waves refract at the Moho, so velocity will increasebecause of the lower Si content (higher density) in the mantle, reaching a seismograph before a slower P-wave remaining in the lower density crust
Cementation
new minerals are precipitated into the void space between sediments
Convergent Plate Boundaries- Volcanoes
Volcanoes at convergent boundaries tend to be composite volcanoes (stratovolcanoes) • If oceanic-continental convergence, lavas are most often andesitic - Fluid-induced melting - rhyolitic can occur under specific conditions • If oceanic-oceanic convergence, lavas are most often basaltic- No continental crust in fluid-induced melting
What is a mineral?
a naturally occurring, inorganic solid that has a crystal structure and a definite chemical composition Ex Gold Not ex: wood, water, steel
Magnetic Chron
a period of normal (black) or reverse (white) polarity
calcile diagnostic property is
a reaction with acid
Peridotite
a rock with low Si, high Fe and Mg
Hot spots
are areas of upwelling magma located in the interior of a plate, not at a plate boundary -Position of volcanic island groups (like Hawaii) trace the direction and speed of the plates over fixed hot spots in the mantle
Sedimentary Basins
are depressions filled with thick accumulations of sediment.
Atomic Mass
atomic number + number of neutrons
Sillica tetrahedra
basic structure of sillicate materials
When oceanic plate meets oceanic
both plates are mafic; so magma is usually mafic
Moho discontinuity
boundary between low-density rocks of the crust with higher density rocks of the mantle
2) Stratovolcanoes / composite volcanoes
built up of layers of lava and pyroclasts - Andesitic lavas plus pyroclastic layers form a tall volcano- Usually associated with subduction zones - Tend to be violent and explosive eruptions - Examples: Mount St. Helens (WA); Cascade Range (WA/OR); Mt Shasta (CA); Fujiyama, Japan
When oceanic plate meets continental, magma begins with mafic composition
but becomes more intermediate/felsic when overlying continental crust is melted
Mudcracks
clayey desiccation features indicating water was evaporated from a lake bed
Mineral Physical Properties
color, hardness, cleavage, luster, density, crystalline form
Limestone
composed of biologically precipitated carbonate mineral calcite CaCO3. There are various types, including: Fossiliferous limestone -- visible fossils Reef limestone -- visible coral reef fossils Coquina -- broken fragments of shell pieces Oolitic limestone -- pearl-like grains (ooids) Chalk -- fine-grained calcite
Two Types of Crust
continental and oceanic
Surface Waves
don't enter Earth's interior
Paleomagnetic Time Scale
established by measuring the magnetic polarity of lava flows of known age
Bowen's reaction series
explains the sequence of fractional crystallization
Sedimentary structures
features in sediments and sedimentary rocks formed at the time of deposition
Depostion
forces of erosion/transport cease and the sediment comes to a rest.
Pillow basalt lavas
form on sea levels
Bedding
formation of parallel layers of sediment as particles are deposited
Ironstones
formed when dissolved iron in low-oxygen environments is later exposed to oxygen and precipitates
Lithosphere
hard, brittle (rigid) solid made of crust and uppermost portion of mantle
Convection
hotter, less dense material rises, while cooler, denser material sinks, then the pattern
P waves velocity _____ with density
increase
Dike
intrusion crosses (not parallel to) the country rock layers ("against the grain") • Neck = dike exposed at land surface
Sill
intrusion parallel to the layering of country rock ("with the grain")
The eruption of Mt Pinatubo ejected so much ash into the atmosphere (blocking the sun's rays) that
it dropped Earth's temperature for over a year
• Large Igneous Provinces
large areas of mafic igneous rocks believed to be caused by hot spots
Batholith
large dome-shaped mound• >100 square km • Frequently form the "cores" of mountains
pahoehoe lava
less viscous "ropey"
Shadow Zones
locations on Earth's surface where no body waves from a particular earthquake can be detected
Siltstone
made from silt; if particles are visible, they are very small and not easy to see
Conglomerate and Breccia
made of gravel sized particles cemented with sand, silt, and/or clay Deposited in very high energy environments: large floods, avalanches
Seismographs
measures and records earthquake magnitude based on the energy released in an earthquake. -P waves arrive first -S waves arrive second -surface waves arrive last
Chert
micro fossils from silica-fixing lifeforms, rather than calcite
Evaporites
minerals left behind salt water evaporates
Mudstone
mix of clay and silt particles
Mineral composition of particles
more = less mineral variety
Rounding of particles
more distance = more rounded
Transport of Sediments: Size of particles
more distance = smaller
Sorting of particles
more distance = well sorted
aa lava
more viscous, sharp jagged
S-Waves indicate
multiple zones within the mantle based on effects of temperature and pressure on peridotite -These velocity changes are not caused by changes in chemical composition
At continental-continental divergent plate boundaries
new oceanic crust is created, but melts overlying continental crust and creates intermediate and felsic compositions
Ophiolite suite
pattern of rocks formed by decompression melting that has since been brought onto land
The boundary between the lithosphere and asthenosphere coincides with melting temperature of
peridotite
Peat
plant remains indentifiable as plant remains
Magmatic differentiation
processes by which rocks of varying mineral composition can arise from a uniform parent magma.
Compaction
removal of air and water in void space between particles -Compaction by
Calcite
reacts with acid
Radical
refers to a compound with a negative charge
Well sorted sediment
refers to sediments with similar size, shape, and mineral composition
Wave speed and arrival times will depend on the
resistance to compression (P) and shear (S) of the material the waves must travel through before reaching the seismograph
Chemical Weathering
rocks are broken apart after changing chemical composition• oxidation, dissolution
Physical Weathering
rocks stripped apart by abrasive stresses• flowing water, wind, frost
Sandstone
sand sized particles; particles are visible
Burial and compaction
sediments are buried under additional sediments over time; enough pressure builds and they become more tightly packed
So how do we know about the interior of the earth?
seismic wave
Laccolith
small dome-shaped mound
Volcanic Ash
smallest pyroclastic fragments; form tuffs and weld together breccias
volcanic ash
smallest pyroclastic fragments; form tuffs and weld together breccias
Asthenosphere
soft, ductile (plastic) solid below the lithosphere
Pyroclasts
solid fragments extruded from volcanic eruption; cause pyroclastic texture Pyroclasts include ash, pumice, fine solidified magma combined into a rock
super continent cycle
splitting of Pangea into two continents; supercontinents form and break over millions of years
Metallic
strong light reflection; looks like a metal
Geoid
the actual shape of the earth
Massive Form
the appearnace of a large mass no obvios appearance of crystal form at macroscale
Moho
the boundary between the earth's mantle and crust
Weathering
the breaking down of rocks into sediments
Streak
the color of a mineral's powder Every mineral will have a diagnostic streak color Minerals of the same color can hvae different streaks
Crystal Form
the growth shape pf a mineral; based on arrangment of atoms Ex: Cubic, Dodecahedral, Octohedral, Prismatic
Atomic Number
the number of protons in the nucleus of an atom
Fractional crystallization
the process by which the crystals are formed in a cooling magma and are segregated from the remaining liquid. Temperature dependent; the first minerals to crystallize from a cooling magma are the ones that are the last to melt.
Viscosity
the resistance of a fluid to flow • High viscosity = more resistant to flow- Flows more slowly, thicker- Example: ketchup • Low viscosity = less resistant to flow - flows more easily, faster- Example: water
Diagenesis / lithification
the sediments become a sedimentary rock
When extrapolating to the core-mantle boundary
the spatial and temporal variations of the magnetic field are more apparent
Bedding plane
the surface separating one bedding layer from another
When P waves abruptly increase to 8 km/s
this signifies the Moho -Indicates thickness of continenetla vs ocean crust -Indicates compostion (low si) of mantle
Igneous Rocks are linked
to plate tectonics
gravity variations affect the geoid
true
Pole migration is caused by
variations of fluid movement in the outer core that affect convection strength
Sillicate group
variety of compounds based on silicon and oxygen -Mafic silicates are erromagnesian (higher in fe and Mg, lower in Si) -Felsic silicates are Non-Ferromagnesian
Bedding sequences
vertically stacked bedding with different types of sedimentary rocks and/or structures in each layer.
Ripples
wave-shaped features showing direction of movement
Seismic Wave
waves of energy produced by an Earthquake
Erosion/Transport
weathered material (sediment) is moved away from source rock and transported to another location• By streams, coastal waves, wind, glaciers
At intraplate hot spots, mantle material directly affects interior of the plateFelsic and intermediate igneous rocks form
when hot spot is under continental crust
Covalent Bond
with electrons shared -atoms share valence (outermost) electrons -By sharing each atom then has stable number electrons Stronger the ionic bond
Yellowstone Supervolcano
• 3 large eruptions in the past 2.1 m.y. • average 730,000 years between eruptions • last eruption 640,000 years ago • Another eruption could have huge effects on agriculture worldwide for at least 1-2 decades • No indications that eruption will occur any time soon!
Sedimentary Rocks
• 5% of rocks in crust • 65% of rocks exposed at land surface • Contain - Evidence of past environments • Oceans, mountains, rivers - Evidence of past climates • Temperature, rainfall, oxygen - Evidence of past animal and plant life• All fossils are found in sedimentary rocks
1980neruptions of Mount Helens Washington
• 63 casualties from lahars (mudslide) that reached almost 50 miles away and destroyed forests in 230 sq mile area• Ash cloud spread over 11 states
Other Mineral Groups
• Carbonates - cation + CO3 - Example: calcite CaCO3 • Sulfates - cation + SO4- Example: gypsum CaSO4 • Sulfides - cation + sulfur (S)- Example: pyrite FeS2• Oxides - cation + oxygen- Example: hematite Fe2O3 • Native elements - mineral composed of single element- Carbon as diamond and graphite- Copper, gold, silver, platinum- Sulfur
Cenozoic Era (the current era)
• Effects of Pangea breakup continues to today - Formation of the Alps • between Italy and France - Formation of the Himalayas • between India and China - Widening of the Atlantic Ocean - Beginning of East African rifting • centered in Ethiopia
Divergent Plate Boundaries
• Fissures at seafloor spreading ridges - Most voluminous volcanic activity • ~ 30,000 miles of ridges on earth - Mostly under oceans - except Iceland - magma typically melted asthenosphere material rich in ultramafic rock (peridotite) - basalt emplaced as new seafloor at spreading ridge or rift • Fissures at continental rifts - Magma melts overlying continental crust, may produce andesite or rhyolite lavas in addition to basaltic - Examples:• East African Rift
Biological sedimentary rocks
• Formed by chemical processes involving living things
Predicting Volcano Eruptions
• Fortunately, in modern times we have a better sense of when a volcano is set to erupt • Precursors that begin to increase leading up to an eruption are clues to increased likelihood of eruption - Seismic activity (earthquakes) - Ground deformation (slope angles, landslides) - Gas emissions - Thermal emissions
Present and Future Volcanic Hazards in the United States
• Hawaii • South-central Alaska & Aleutian Island chain • Cascade Range - Washington, Oregon, northern CA, southwestern Canada • Yellowstone Supervolcano - Wyoming, Montana
Locations where sediments are deposited: Continental
• Higher-energy transport • Coarser grain sizes deposited
Rhyolitic Lavas
• Highest silica content, viscosity • Common where magma melts large quantities of continental crust
Basaltic lavas
• Highest temperature (1000−1200ºC) • Lowest viscosity • Form basalt igneous rock (mafic)
Andesitic Lavas
• Intermediate silica content, viscosity • Common at subduction zones
Andesitic lavas
• Intermediate viscosity, temperature • Form andesite igneous rock (intermediate)
Micas
• KAl2(AlSi3O10)(OH)2 • Muscovite (lighter) • K(Mg, Fe)3AlSi3O10(OH)2 • Biotite (darker) • 1 cleavage plane • 3 oxygens shared = stacked sheets of tetrahedra
Locations where sediments are deposited: Marine (sea/ocean)
• Lower-energy transport • Finer grain sizes deposited
Rhyolitic lavas
• Lowest temperature (600-800ºC) • Highest viscosity • Form rhyolite igneous rock (felsic)
Intraplate Volcanism
• Magmas associated with a mantle hot spot in an oceanic crust produce shield volcanoes of basaltlava - Example: Hawaii • Magmas associated with a mantle hot spot under continental crust will produce more felsic lavas; often as explosive eruptions- Example: Yellowstone Supervolcano
Lines of evidence that led to Plate Tectonic theory:
➢Sea floor mapping ➢Topography ➢Locations of earthquakes and volcanoes ➢Sea floor ages ➢Paleomagnetism / magnetic pole reversals